Ochatoxins belong to a family of mycotoxins that are secondary metabolites of Aspergillus sp. and Penicillium sp. Their growth promoting conditions are delineated in Table 1.

Several types of ochratoxins occur naturally, namely, ochratoxin A, ochratoxin B (dechlorinated OTA) and ochratoxin C (ethylated OTA), and are often co-produced. Ochratoxin A (Figure 1) is the most prevalent toxin and is classified as a group 2b potential human carcinogen by the International Agency for Research on Cancer [1]. Aristolochic acids are phytotoxins belonging to the Aristolochiaceae family of plants and have been suspected to induce similar nephrotoxic effects in humans and animals [2].

Ochratoxins occur primarily in cereals in northern Europe and Africa. A few examples of foods containing ochratoxins are listed in Table 2.

Analysis of OTA and citrinin in food and feed samples were performed by enzyme immunoassays, which gave detection limits of 0.5 and 5 ng/g, respectively. OTA-values were confirmed by high performance liquid chromatography after immunoaffinity chromatography. Vrabcheva and co-workers [3] found the highest toxin levels in wheat, wheat bran, and oats. South African wines tested (15 white and nine red) were found to contain detectable levels (>0.01 μg/L) of OTA, with a mean of 0.16 μg/L in the white wines and a mean of 0.24 μg/L in the red wines [5]. Ochratoxins have also been found in meat, dairy and baked products, especially swine sausages and breads [7,8]. In humans a dietary intake of 1.21 µg per day has been linked to endemic nephropathy [7]. Further reports suggest that chronic dietary exposure to OTA, a mycotoxin frequently detected in various food items may be linked to the pathogenesis of endemic nephropathy, a chronic tubulointerstitial kidney disease which occurs in geographically limited areas of the Balkan region [8]. Contradictory findings have been reported by Mally and co-workers [9]. Based on food consumption data and OTA serum concentrations, they suggest that human exposure, even in areas with relatively high dietary exposure to OTA, such as endemic villages, is several orders of magnitude below doses known to cause nephrotoxicity and tumour formation in laboratory animals.

Ochratoxins have been related to human and animal diseases in literature especially since the early 1970s. Most reports indicate that ochratoxin plagued especially the North Eastern European countries, such as Bulgaria, Romania, Serbia, Croatia, Bosnia, Herzegovina, Slovenia, Macedonia, Monte Negro and Africa, such as Congo, South Africa, Tunisia, Morocco and Egypt [3,4,5,6,7,8,9,10,11].

The concentration range of OTA in human serum is 5–50 ng/mL and OTA has a long serum half-life in various species including humans [3]. Schwerdt and others [12] measured OTA concentrations in blood of subjects suffering from various renal diseases as e.g. interstitial nephritis or mesangial proliferating glomerular nephritis and compared these values with those obtained from healthy individuals. OTA was detected in 87% of all samples. There was no significant difference between OTA concentrations of healthy individuals and patients with chronic glomerular nephritis whose sera showed OTA concentration greater than 1.5 nmol/L. In contrast, no values greater than 1.5 nmol/L were present in the sera of patients with membranous or focal-sclerotic glomerular nephritis. These preliminary results suggest that a serum concentration of OTA greater than 1.5 nmol/L may be a biomarker for glomerular nephritis.

In May 2000, Abouzied and colleagues [7], using a competitive direct enzyme-lnked immunosorbent assay for OTA (detection limit 1 μg/kg), investigated OTA contamination in 165 samples of home-produced food (beans, potatoes, corn, wheat, flour) and feed from households in villages from the Balkan endemic nephropathy region (Vratza district) of north-western Bulgaria. Samples were collected from: (a) 20 households of Balkan endemic nephropathy villages (n = 8), and 16 households of Balkan endemic nephropathy-free households (within-village household controls) and (b) 22 Balkan endemic nephropathy-free households of Balkan endemic nephropathy-free villages and 22 households between-village controls. Balkan endemic nephropathy households consistently had a higher proportion of OTA-positive samples than within village control households, but similar (for some foods) or lower (for other foods) amounts when compared between village controls. The proportion of OTA-positive samples was also higher in household between village controls when compared to those within village controls. Furthermore, Balkan endemic nephropathy households had a similar number of OTA-positive samples when compared to the pooled values for within and between groups of households. OTA-exposure estimates, derived from our OTA-concentration findings and the reported average per capita monthly consumption of basic foods in rural Bulgaria, showed the highest OTA intake in Balkan endemic nephropathy households (1.21 μg per day), vs. 1.03 μg per day in between village control households, and 0.71 μg per day in within village control households. This is in agreement with other studies carried out in the same region [4,13]. These OTA intakes are higher than those reported in the European Union, and are close to the upper limits acceptable to several food-safety organizations. These data indicate that OTA may not alone cause Balkan endemic nephropathy but synergistically with other environmental toxicants and/or predisposing genotypes. Peraica et al. [14] recently detected OTA in food collected in the endemic areas and in blood and urine of their residents. In Serbia, a survey showed the prevalence of OTA in Balkan endemic nephropathy families associated with the presence of citrinin [15].

Studies have reported that the pathological changes produced by aristolochic acid are comparable to those produced by OTA [2]. There is therefore the need for toxin co-occurrence studies involving citrinin, fumonisin, aristolochic acid and OTA. Co-contamination of ochratoxin A and citrinin was found in varying number of households in two Balkan villages. Citrinin levels in those samples were clearly higher than those of OTA [15,35]. Data on the co-occurrence in food of OTA and other toxic mycotoxins such as citrinin and fumonisin B1 have been reported also [8,14]. Cultured cells and laboratory animals treated with combinations of OTA and other nephrotoxins, show synergistic effects [8]. The occurrence of OTA- and either citrinin or fumonisin increased genotoxicity [14,35].

Despite many efforts, the aetiology of endemic nephropathy is still unknown [14]. This disease occurs in the rural population of geographically limited areas of Bulgaria, Bosnia and Herzegovina, Croatia, Romania, and Serbia, and a number of theories have been proposed about its aetiology. The mycotoxin theory has prevailed until now, based on the studies of nephrotoxic mycotoxin OTA that revealed higher frequency of OTA-positive food and blood samples in endemic than in non-endemic Balkan areas. However, recently it has been suggested that aristolochic acid is the aetiological cause of endemic nephropathy, because of the histological similarities in kidney lesions between patients suffering from endemic nephropathy and patients suffering from Chinese herbs nephropathy caused by aristolochic acid. Until now it has not been unequivocally proved that the inhabitants of endemic nephropathy areas are exposed to higher concentration of aristolochic acid than in other regions and the exposure pathways are rather uncertain. There is a paradox between the wide distribution of OTA throughout the world with the expected risk of OTA causing human renal disease and the rarity of reported cases demonstrating its role in chronic renal disease [32]. OTA and probably other mycotoxins could be major environmental factors in the occurrence of renal disease especially in developing countries according to Tatu and co-workers [40]. Some studies have found a geographic co-variation between OTA content in food/feed and Balkan endemic nephropathy manifestation; others have not [7]. The Romanian group [40] mention two actually competing theories attempting to explain the cause of Balkan endemic nephropathy: (1) the mycotoxin hypothesis, which considers that Balkan endemic nephropathy is produced by ochratoxin A ingested intermittently in small amounts by the individuals in the endemic regions, and (2) the Pliocene lignite hypothesis, which proposes that the disease is caused by long-term exposure to polycyclic aromatic hydrocarbons and other toxic organic compounds leaching into the well drinking water from low rank coals underlying or proximal to the endemic settlements. In this review we have outlined the current knowledge on ochratoxins. Future studies need to focus on possible factors and co-factors involved in aetiology of OTA renal disease and cancer.